Method and apparatus for television transmission



Nov. 23, 1937. H. A. IAMS METHOD AND APPARATUS FOR TELEVISIONTRANSMISSION Filed March so, 1933 //V VEN TOE Harley .59. 1211125, l

UNlTED STATES PATENT OFFICE METHOD AND APPARATUS FOR TELEVISIONTRANSRIISSION Harley A. Iams, Collingswood, N. J., assignor to RadioCorporation of America, a. corporation of Delaware Application March so,1933, Serial No. 663,450

7 Claims.

My invention relates to improvements in methods and apparatus fortelevision transmission.

During the presentation of television programs, the transmitting stationhas, heretofore, been identified either by placing in the transmittingapparatus a suitable slide or plate containing the station call letters,or by making an announcement by voice such as in the usual broadcastprograms. It is seen however, that it would be advantageous to have thetransmitting station constantly identified at the receiving points, andit is one of the objects of my invention to provide an improved methodof operation and apparatus for such purpose.

Another object of my invention is to provid an improved method andapparatus for television transmission whereby any desired representationmay be transmitted independently of the transmitted object, therepresentation being station letters, advertising slogans or any otherdesired information.

Other objects and advantages will hereinafter appear.

In accordance with my invention, a cathode ray tube, provided withphotosensitive mosaic screen structure onto which an image of the viewfor transmission is projected, is utilized for developing the picturesignals, and a portion, of the photosensitive area of the screenstructure is utilized for developing signals independently ofdevelopmentof the picture signals. The independently developed signals, whenreceived, cause reproduction of the representation referred to.

More particularly. in accordance with my invention, the call letters ofthe transmitting station are transmitted continuously and independ entlyof occurring changes in the transmitted view by placing in front of thephotosensitive surface of a cathode ray transmitting tube a mask shapedto make the station call letters. This mask is placed at a corner of thephotosensitive screen structure, and prevents the cathode ray fromscanning the masked part of the photosensitive area.

In another form of my invention, wherein picture signals are developedby projecting an image of the view onto a photosensitive, mosaic screenin a cathode ray tube, an image of the call letters of the transmittingstation is projected independently onto a corner of this structure.

In still another form of my invention, the call letters of thetransmitting station are painted, scratched or otherwise applieddirectly upon the photosensitive screen structure of a cathode raytransmitter tube when apparatus of this type is used for developing thepicture signals.

My invention resides in the improved method of operation and apparatusof the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof isshown in the drawin wherein Figure l is 'a perspectivediagrammatic Viewof television transmitting apparatus embodying and operating'inaccordance with my invention;

Fig. 2 is a. simplified perspective view, showing another way ofpracticing my invention; and

Figs. 3 and 4 are front elevational views of photosensitive screenstructure for use in a cathode ray transmitter tube, illustratingfurther modifications.

In Fig. 1, the reference numeral designates a cathode ray transmittertube comprising screen structure l2 having a photosensitive, mosaic area[4. Suitable means, in the form of a gun l6, operates to develop a rayl8 of electrons and to direct the same at the screen structure I2. Forthe purpose of causing the ray to scan the screen structure, it isdeflected horizontally at a relatively high rate and is deflectedvertically at a relatively low rate, depending upon the number of framesrequired per second.

Horizontal deflection of the ray is efiected by causing a saw-toothcurrent wave at the required frequency to pass through deflecting coils26. Vertical deflection of the ray is effected by causing a saw-toothcurrent wave at the required frequency to pass through deflecting coils22.

Since the method and mechanism for projecting an image of the View orobject onto the photosensitive area forms no part of my presentinvention, no detailed explanation thereof is believed to be necessary.

As the ray l8 scans the photosensitive area I, picture signals aredeveloped in the output connection 26 which supplies the usual amplifierand transmitter 28, as disclosed in the co-pending application of Ray D.Kell, Serial No. 649,766, filed January 3, 1933 and assigned to RadioCorporation of America.

It has been found that when the ray is interrupted by some means, suchas a piece of metal, a signal is produced in the amplifier similar tothat which would be produced for a bright spot on the transmittedobject. In the embodiment of my invention shown in Fig. 1, this actionis made use of by interposing a. metallic mask 30 between the lowerright hand corner of the photosensitive s a ea i i and the electron gunH6. The mask may be carried at the end of a wire 32 extending outwardlyfrom and afllxed to the screen structure I! whereby the mask issupported in close proximity to the photosensitive area. The mask may bein the form of a single letter, as shown, or may comprise a number ofletters, numerals, or other configurations which, when reproduced at thereceiving points, identify the particular transmitting station.

In operation, the mask 30 prevents the electrons in the ray frombombarding that portion of the photosensitive area directly back of themask. The signals thereby developed operate to reproduce at thereceiving points a bright representation having the same configurationand extent as the mask 30. When the receiving apparatus is in the formof a cathode ray tube having a fluorescent screen which is scanned by acathode ray in the same manner in which the ray l8 scans the screenstructure I2, a bright letter or other representation of the same shapeas the mask 30 .will appear in the lower right hand corner oi thefluorescent screen.

With reference to Fig. 2, the same effect and result is obtained as inFig. 1 by projecting an image of the required representation onto thephotosensitive area M. This is done by a suitable i'orm of projectingapparatus 34 into which a slide is placed containing the station callletters, advertising matter or other information or representationdesired. -It is to be noted that projection of the image of the requiredrepresentation is entirely independent of projection of the image of theview or object 24 onto the photosensitive area I4. As in Fig. l, therequired representation is continuously transmitted and reproduced atthe receiving points independently of occurring variations of conditionsof light and shade over the object or view.

If the photosensitivity of the screen structure I2 is reduced, a signalis produced the same as if there were at that instant a dark spot on theobject. This action is utilized in the modification shown in Figs. 3 and4. In Fig. 3, the station call letter or letters, or any representation36 desired, is painted on the photosensitive surface l4. When the rayscans the painted portion, therefore, the effect is to causereproduction at the receiving point of a dark figure having the sameconfiguration as the figure 36. In Fig. 4 the action and result is thesame as in Fig. 3, except that the representation 36a is made byscratch-' ing away the photosensitive material.

It will be understood that other modifications oi. my invention withinthe conception of those skilled in the art are possible withoutdeparting from the spirit of my invention or the scope of the claims.

I claim as my invention:

1. In a television transmission system of the cathode ray type, acathode ray optical image translating tube, means for projecting anoptical image thereupon for transmission, said tube be,. ing providedwith a source of cathode rays and a photosensitive light translatingtarget of which predetermined areas within the picture signal developingsection of said target have different electrical characteristics forproducing substantially fixed electrical output effects irrespective ofconditions of illumination of the entire screen, means for causing theoath-ode ray to scan the target. and means for producing from thescanning a series of image signals representing both the optical imageand a modification thereof as determined by the scanning of the areas ofdifferent electrical properties from the projected optical image uponthe light translating target area.

2. In a. television transmission system 0! the cathode ray type, acathode ray optical image translating tube, means for projecting anoptical image thereupon for transmission, said tube being provided witha source of rays and a target surface embodying photosensitive lighttranslating portions and predetermined areas within the picture signaldeveloping section of said target having diflerent electricalcharacteristics from t e light translating portions so as to producesubstantlally fixed electrical output eifects irrespective of conditionsof illumination oi. the entire screen, means for causing the cathode rayto scan the target, and means for producing from the scanning a seriesof image signals representing both the optical image and a modificationthereoi as determined by the scanning of the areas of differentelectrical properties from the projected optical image light translatingtarget area.

3. The method of multiple signal translation which comprises the steps01' projecting a light image upon a light sensitive plane to produceelectronic emission proportional to the brilliance of the light imagescanning the plane oi. projection to produce electrical signalsrepresentative of the projected light image, controlling independentlyoi the projected light image the electronic emission within a selectedportion of the projected optical image area to vary by predeterminedvariations the series of produced electrical signals, and producing atrain of image signals representing the optical image projected upon theplane and modified by the controlled emission.

4. The method of multiple signal transmission which comprises projectinga light image upon a photosensitive surface to produce from the surfaceelectronic emission proportional to the brilliance of the light image toproduce thereby an electrical image of the light image, scanning theproduced electrical image to produce electrical signals representativeof the projected light image, controlling independent of the projectedlight image the electron emission from predetermined areas of thephotosensitive surface within the areas over which the light image isprojected during scanning of the electrical image formed by the opticalimage upon the photosensitive area to vary thereby, by predeterminedamounts, the produced electrical signals.

5. The method of multiple signal translation which comprises the stepsof projecting an optical image for transmission upon a light sensitiveplane to produce normally over the entire area electronic emissionproportional to the brilliance of the light image scanning the plane ofprojection to produce electrical signals representative of the projectedlight image, controlling independently of the projected light image theelectronic emission over selected portions within the area over whichthe optical image is projected to vary by predetermined variations theseries of normally produced electrical signals and transmitting theresultant signals to cause at points of reception the conversion of thesignals into an electro-optical image.

6. In the art of a television system, the method of operation whichcomprises projecting onto a given area a photosensitive screen structurean optical image of a subject for transmission so as to produce electronemission from the screen, scanning the area of said screen structure todevelop picture signals representative of conditions of light and shadeat the respective elemental areas of the optical image and effective ata receiver to produce an image of said subject, developing over aportion of the photosensitive area within that portion of the saidscreen structure subjected to the optical image and independent of anyconditions of illumination thereof a second series of signalsintermingled with the first series and eflfective at the receiver tubeto modify in a visible manner the optical representation resulting fromthe translation of the series of signals due to the image of saidsubject into electro-optical representations.

7. In a television transmitting system, a cathode ray tube, aphotosensitive light translating screen provided within the tube, meansfor projecting an optical image upon the photosensitive screen, saidscreen also having predetermined areas thereof within the boundariesover which the light image is projected of difierent electricalcharacteristics from the photosensitive light translating portion, meanswithin the tube for deveioping a cathode ray beam, means for causing thedeveloped cathode ray beam to scan the screen within the tube, anexternal circuit wherein picture signals are developed for transmissionin accordance with the scanning of the screen structure by the cathoderay beam, and means for causing during the scanning operation signals tobe developed in the external circuit which are representative of theoptical image and modifled during predetermined time periods by a seriesof signals of predetermined amplitude de- I veloped upon scanning thescreen and completely independent of the signals due to any projectedoptical image upon the photosensitive screen.

HARLEY A. IAMS.

